In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), lithography is used to obtain patterned structures of various materials such as insulators, semiconductors and/or metals in a sequence leading to the achievement of the desired structure.
Most lithographic processes (excluding so-called direct-write techniques) typically employ some type of patterned mask through which the imaging radiation is projected onto the resist material to be patterned on the substrate of interest. Typically, the mask itself is formed by a lithographic technique such as direct-write electron beam lithography or in some instances by projection UV lithography (especially deep UV—248 nm) using an appropriate resist material. Typically, the mask comprises a patterned metal layer(s) (e.g., chromium) on a quartz plate (or other transparent plate).
The introduction of chemically amplified (CA) resist for electron beam lithography has reduced the writing time dramatically for mask making, however, for low pattern density circuitry, it would still take a long time to write the images using positive resist. Therefore, it is more desirable to have negative tone system for electron beam lithography. Most traditional negative tone CA resists are using phenolic polymers as base resin. Phenolic systems are usually too high in dissolution rate in the 0.263N TMAH developer that has become standard in the industry. Other known negative resist systems are often prone to excessive microbridging.
Thus, there is a need for improved negative tone resist compositions especially suitable for electron beam lithography, as well as for lithographic processes employing such resists to create patterned material features, especially in the context of making lithographic masks.